In a silver halide photographic element, a color image is formed when the element is exposed to light and then subjected to color development with a primary aromatic amine developer. Color development results in image wise reduction of silver halide and production of oxidized developer. Oxidized developer reacts with one or more incorporated dye-forming couplers to form an image wise distribution of dye. Dye-forming couplers (as well as other various photographic addenda) are typically dispersed in silver halide emulsion layers of the photographic element with the aid of coupler solvents, which are typically oily or low melting compounds.
In any polychromatic chromogenic photographic material, it is desirable that the dyes so formed should have certain properties. For instance, the dyes should be bright in color with very little secondary absorption so that good color reproducibility is obtained. The stability of image dyes generated on chromogenic development often does not meet performance expectations. These expectations include resistance to light fade and both humid and dry heat dark fade. The dyes that are formed by any color coupler during processing have a tendency to fade over time as a result of exposure to light, heat, humidity and oxygen resulting in a deterioration of the original recorded image. It is therefore highly desirable that the formed dyes should be resistant towards fading by heat, humidity and light.
Techniques are known in the art for providing resistance to light fade of photographic dyes. Unfortunately, these techniques have not been completely successful resulting in the development of many unique stabilizing chemistries. Compounds which have been disclosed as light stabilizers image dyes, e.g., include substituted phenolic and blocked phenolic compounds including; heterocyclic phosphorous materials (U.S. Pat. No. 4,749,645), substituted and blocked bisphenols (UK 1,267,287, U.S. Pat. No. 4,782,011, DE 4,307,439, DE 4,307,439, DE 4,320,828, EP 0 508 398, EP 0 538 862, U.S. Pat. No. 5,294,530, U.S. Pat. No. 5,426,021, U.S. Pat. No. 5,441,855, U.S. Pat. No. 5,441,861, U.S. Pat. No. 5,466,569, U.S. Pat. No. 5,891,613, WO 91/008,515, U.S. Pat. No. 5,567,578, U.S. Pat. Nos. 5,284,742, 5,091,294, EP 0 310 552, U.S. Pat. No. 5,935,773). In addition, dyes may also be stabilized against fading by light with the use of aromatic thiomorpholine dioxide compounds as described in EP 1 116 99, U.S. Pat. No. 5,561,037, EP 457,543, EP 310,552, EP 310,551, EP 397,050, EP 393,718, U.S. Pat. No. 5,360,711; and various sulfonamido compounds (U.S. Pat. No. 6,140,031, U.S. Pat. No. 6,071,686, U.S. Pat. No. 6,013,429). German patent application DE 1 96 32927 describes the use of cyclic imides, cyclic carbamates, and cyclic ureas as a means of improving the chromogenically developed color image dye stabilities. However, in particular, the amount of dye stabilization to light fade is only modest. U.S. Pat. No. 5,352,572 reports the use of a specific bis-urea compound in combination with malonamide yellow couplers. However, the bis-urea was not shown to be effective for other couplers and was specifically reported to be ineffective for beta-ketoamide yellow couplers. U.S. Pat. No. 6,045,987 describes the use of amide group substituted aromatic compounds, wherein the amide groups are directly bonded to a phenyl ring, as addenda to coupler dispersions, and in particular the use of such compounds in association with magenta and cyan dye image-forming couplers. U.S. Pat. No. 6,413,707 discloses the use of urethane compounds and U.S. Pat. No. 6,555,306 describes the utilization of a substituted dipiperidine compound as coupler solvents in photographic elements to improve image dye stability. Most recently aliphatic bis-amide compounds have been patented as light stabilizing yellow coupler solvents (U.S. Pat. No. 6,846,620).
Various stabilizers classes have been chemically bonded together to form combination stabilizers. For example, thiomorpholine dioxide stabilizers have been linked to sulfonamido stabilizers (U.S. Pat. No. 6,140,031) and phenolic stabilizers have been bonded to Hindered Amine Light Stabilizers (U.S. Pat. No. 4,584,265).
It is still desirable to improve on the light stabilization of dyes beyond that afforded with use of the above stabilizers. Ra rely mentioned is the lifetime of an individual stabilizer itself. Theoretically if the stabilizer is consumed during the process, at some point the system will fail due to lack of stabilizer. For example, hindered phenolic antioxidant have a turn over number of four at their greatest [Ohkatsu, Y., Matsuura, T., and Yamato, M.; Polym. Degrad. And Stab., (2003), 81, 151–156]. This means a phenolic stabilizer will only go through the stabilizing process a maximum of four times before it is consumed. It would be advantageous to have a method to increase the lifetime of the stabilizer, the result of which would lead to an increase in the lifetime of the dye imaging system.
Energy dissipation is a well-known mechanism of action in certain compounds capable of protecting molecules against decomposition by light, such as ultraviolet light absorbers (UVA's). They absorb unwanted UV energy and then dissipate this energy via heat release or other harmless mechanisms to return the excited molecule back to its ground state. Cinnamates are one class of UV absorber utilized in many commercial sun block cosmetics. For example, ethylhexyl-p-methoxy cinnamate, Parsol MCX (CAS 5466-77-3), is one most commonly utilized. Cinnamates are known to dissipate energy through an efficient reversible cis/trans photoisomerization reaction. The E to Z and Z to E isomerization is not far from unity. Cinnamates have been patented as UV absorbers for photographic uses (U.S. Pat. Nos. 3,705,805; 3,707,375).
In spite of the above attempts to improve dye stability, further improvements are still needed to stabilize image dyes against light exposure.